This invention relates in general to electrical devices employed for protection of alternating current networks.
In electrical quantity sensing devices of the prior art, the current information and relay circuit operating power was derived from two current transformers. Under some conditions at least one of the transformers was designed to saturate within the expected range of the current magnitudes. Other prior art devices utilized a current transformer in combination with a separate power source.
In static time delay relay circuits of the prior art it is common to employ a curve shaping device for providing relay characteristics similar to those of prior widely used electromechanical devices. Curve shaping arrangements are illustrated in U.S. Pat. No. 3,496,417 to N. D. Tennebaum dated Feb. 17, 1970; and U.S. Pat. No. 3,544,846 to F. T. Thompson dated Dec. 1, 1970.